The maintenance of mitochondrial size in the rat adrenal cortex zona fasciculata by ACTH

Abstract

An electron microscopic examination of the rat adrenal cortex reveals changes in the abundance and structure of the mitochondria of the zona fasciculata after hypophysectomy, which are time-dependent and lead to the production of giant (diameter > 1.5μ) mitochondria. These changes were measured in low power fields involving a total thin section area of 850 μ 2 at 4, 7, 11, and 14 days after hypophysectomy. Following hypophysectomy, the number of mitochondria decreases, the volume of lipid droplets increases, the ratio of the surface area of the outer mitochondrial membrane to the mitochondrial volume decreases (indicative of increased size), and the percent of small mitochondria increases. The volume of giant mitochondria, comprising 8% of the total mitochondrial volume in control animals, increases to 65% of the total 7 days after hypophysectomy and to 82% 14 days after hypophysectomy. It has been found that administration of ACTH causes the gradual reversal of these effects of hypophysectomy over a period of 9 days. Mitochondrial partitions, clearly associated with the inner membrane, were observed after hypophysectomy and during ACTH-induced recovery. The evidence suggests that ACTH controls the process of growth and division of the mitochondria. The retarded growth of mitochondria in the absence of ACTH is associated with fusion of existing mitochondria to form giant mitochondria.